It is known at present to reproduce images by a photographic means using a photosensitive composition composed of a mixture of a polymerizable compound having an ethylenically unsaturated bond, a photopolymerization initiator, and, if necessary, a proper binder having a film-forming faculty and a thermopolymerization inhibitor. That is, as described in U.S. Pat. Nos. 2,927,002, 2,902,356 and 3,870,524, since such as photosensitive composition is hardened and insolubilized by the irradiation of light, a hardened image of a desired photosensitive composition can be formed by forming a proper film or layer of the photopolymerizable composition, light-irradiating the layer through a desired negative image, and then removing the layer of the photopolymerizable composition only at the unexposed areas, by a proper solvent. The photopolymerizable compositions of this type are, as a matter of course, very useful as materials for forming photosensitive printing plates, photoresists, etc.
A conventional polymerizable composition itself having an ethylenically unsaturated bond has an insufficient light-sensitivity. Accordingly, in order to increase the light sensitivity of the polymerizable composition, the addition of a photopolymerization initiator has been proposed. Examples of photopolymerization initiators used for this purpose include benzil, benzoin, benzoin ethyl ether, Michler's ketone, anthraquinone, acridine, phenazine, benzophenone, 2-ethylanthraquinone, etc. Photopolymerization initiator capable of providing a high light sensitivity include known quinazoline derivatives disclosed in Japanese Patent Application (OPI) No. 53747/82. (The term "OPI" indicates an unexamined published patent application open to public inspection). However, even when using these photopolymerization initiators, the inductivity of the photopolymerizable composition to hardening remains low and hence it requires a long time for image exposure when forming an image. Accordingly, there are problems such as when forming a precise image, an image having good quality is not reproduced if there is even slight vibration during operation, the amount of the energy radiation of a light source for exposure must be increased, which results in emitting a large amount of heat, and further the layer of the photopolymerizable composition is liable to deform or denature due to the heat.